Why there is a layer of transparancy on my uv map?
First question around transparency: When Blender exports a UV map, faces are slightly opaque by default. This is so people can more clearly distinguish the difference between what IS a face, and what isn't. Ordinarily the UV map is taken into a graphic program like GIMP, Photoshop, illustrator, etc as a layer: the actual artwork is drawn on different layers, and that final result is exported as a Blender compatible file format, WITHOUT the original underlying (or overlying) UV map.

So... export your UV map, do your artwork, and remove the UV map layer before saving your finished art.

The amount that Blender will tint faces is configurable! When exporting, look in the left column for this palette:



...And adjust the Fill Opacity to zero.

Your second question needs more detail, such as which render engine you're using (Blender Internal or Cycles [or other]), what node you're adding to color it and how the nodes are connected. A screenshot would be necessary. Good luck :)